1. Field of the Invention
The present invention relates to signals, in particular, Light Emitting Diode (LED) Signals. More specifically, the present invention relates to an LED traffic signal having a LED light output degradation sensing circuit that activates a visible fault mode.
2. Description of the Related Art
LED traffic signals present numerous advantages over common incandescent lamp traffic signals. Use of LED""s provides a power consumption savings and extremely long life in comparison to common incandescent light sources. The long life span creates improved reliability and sharply lowered maintenance costs.
LED signals have an extremely long service life that has increased with each new generation of LEDs. Incandescent lamps, while having a much shorter service life, have relatively constant light output until a total failure occurs, i.e. burnout of the light filament. LED signals, over an extended period, have gradually diminishing light output. Further, LED light output is negatively affected by temperature. In extreme climate or during unnaturally warm periods LED light output diminishes during the day and then returns to a normal level during cooler periods at night.
Because of the difficulty, time and expense of accurately determining when an LED signal has permanently dropped below the acceptable light output limit, it is customary for consumers to automatically replace LED signals upon expiration of the warranty (for example, five years). This may result in years of useful service life being unnecessarily wasted, reducing the cost effectiveness of using LED signals.
U.S. patent application Ser. No. 09/543,240, assigned to Gelcore LLC, incorporated herein by reference, discloses monitoring circuits for an LED signal that shut off the signal if the power supply or LED arrays change their voltage and/or current characteristics. Unfortunately, LED light output may degrade without a change in the LED signal""s voltage or current characteristics.
U.S. patent application Ser. No. 09/827,429, assigned to Gelcore LLC, filed Apr. 6, 2001, incorporated herein by reference, discloses light output monitoring circuits for an LED signal which disables the signal when a low light output threshold has been reached. Unfortunately, disabling an LED signal, for example a traffic signal, can have an extremely disruptive effect that will last until materials and personnel become available and the failed signal is replaced.
Therefore, the present invention has the objective of providing a cost effective and automatic means for detecting when an LED signal""s light output has fallen below an acceptable level, and then initiating a visible failure mode while still continuing to operate.
Further objects will be realized by one skilled in the art, through review of the following description and appended claims.
A light sensor, mounted within an LED signal housing, senses a light output level. When the light level falls below a preset level, a short circuit is created that disables a selected group of LEDs. The disabled LEDs creating an altered display aspect that alerts users that replacement is necessary, but permits signal operation until replacement occurs.